This invention relates to alternating current generators and more specifically to alternating current generators having magnetic claw-pole segments, permanent magnets interposed between adjacent pole fingers and a flux controlling field coil. Such alternating current generators are hereinafter referred to as hybrid generators.
Examples of such hybrid generators are found in U.S. Pat. No. 4,959,577 to Radomski and assigned to the assignee of the present invention. A conventional stator comprising a multi-phase output winding and magnetic material laminations is supported by a housing. Further, the hybrid generators utilize a Lundell rotor that is comprised of two claw-pole members having interleaved pole fingers and a field coil surrounding a magnetic core therebetween the claw-pole members. The claw-pole members, magnetic core and field coil are supported by a rotor shaft and are secured thereto. Opposite ends of the shaft are supported by bearings and the assembly is free to rotate within the stator with minimal clearance between the rotor and stator. Slip rings are secured to the shaft and in operation couple the field coil to a current source via contact brushes. A plurality of permanent magnets are disposed between adjacent claw-pole fingers. When the field coil is not energized, the magnetic flux developed by the permanent magnets is shunted through the rotor assembly. However, when the field coil is energized, the magnetic flux developed by the permanent magnets additively contributes to flux across the stator/rotor air gap resulting from field coil excitation.
The permanent magnets are fitted into grooves or slots formed along the opposing side surfaces of adjacent claw-pole fingers. Further, a suitable adhesive may be used to secure the permanent magnets to the claw-pole fingers. Such an assembly requires significant machining of the claw-pole members and strict dimensional control to assure appropriate magnet retention without undue stress to the permanent magnets which tend to be brittle. The use of adhesives as retention means for the magnets disadvantageously requires fixturing of individual magnets, allowances for curing time and is cumbersome in a mass production environment. Furthermore, the adhesives must be able to withstand the swings in thermal loading typically experienced in alternating current generators. A dozen individual permanent magnets are required in a typical six finger claw-pole rotor. Since individual handling of the permanent magnets is required the assembly process is even more cumbersome, expensive and subject to variations in build quality.